The U.S. Air Force flight-tested an unarmed Mk21A reentry vehicle aboard a Northrop Grumman Minotaur I rocket on Oct. 9, 2026, from Vandenberg Space Force Base, California, the Air Force Nuclear Weapons Center (AFNWC) announced. The test was described as an in-flight environmental test supporting development of the reentry vehicle, which is designed for the future LGM-35A Sentinel intercontinental ballistic missile.
The launch was overseen by the U.S. Space Force’s Rocket Systems Launch Program. AFNWC said Minotaur launch vehicles support testing and demonstration of new payload technologies in operationally realistic environments. The Mk21A is under contract with Lockheed Martin for its engineering and manufacturing development phase.
Maj. Gen. William Rogers, the Air Force’s portfolio acquisition executive for ICBMs and AFNWC director of ICBM systems, said the Mk21A is “crucial to modernizing our ICBMs in response to the rapidly changing global threat picture posed by our adversaries.” He added that the reentry vehicle’s development “will ensure a safe, secure and effective deterrent for generations to come.”
Brig. Gen. Amanda Okeson, program manager at AFNWC’s ICBM Systems Directorate, said “investment in modernization of the ICBM mission remains a top priority for the Air Force.”
This was not the first Mk21A test aboard a Minotaur I. A previous trial took place from Vandenberg SFB on June 17, 2024. The latest press release did not include an image of the Oct. 9 test, instead sharing a picture from the 2024 launch.
The Mk21A is being developed to accommodate the W87-1 nuclear warhead for the Sentinel program. AFNWC awarded Lockheed Martin a $996 million contract for the Mk21A in October 2023, followed by a $453 million contract modification in November 2025. A Pentagon acquisition report released in September said the modification was part of a new baseline intended to “decouple [the Mk21A’s] schedule from external programs and continue development with an updated, more resilient plan.”
The test follows the vertical stacking of the first Sentinel ICBM at Vandenberg SFB in September 2026, in anticipation of its first test launch next year. A Critical Design Review for the entire Sentinel system is scheduled by March 2027.
Sources: Air & Space Forces Magazine · The Aviationist